The present invention relates to gaskets and especially to high temperature gaskets such as head gaskets to be used in sealing the head and block of an internal combustion engine, as well as to other gaskets used in association with such engines, particularly where high service temperatures are encountered. Gaskets used in environments where high service temperatures are encountered, as in air compressors, may also be produced in accordance with this invention.
The sealing of an internal combustion engine is a complex and difficult matter. High temperatures and pressures which are localized and which vary across the surface of the gasket between the block and the head require differing treatments at different areas, and usually require the use of sealing aids such as grommets, elastomeric seals, armoring and the like. High temperature engineering resins and composites have been suggested for use for head gaskets, for example in U.S. Pat. No. 4,817,969.
In U.S. Pat. No. 4,817,969 a sealing bead which is integrally formed with the gasket body is provided. The bead is preferably trapezoidal in cross-section and extends above the surface of the main body a distance of from about at least 5% to about 15% of the thickness of the main body. Desirably a pair of recesses are provided in the main body at the base of and immediately adjacent to the sealing bead. The recesses accommodate some flow of the resin forming the bead under high sealing loads to reduce the possibility of stress-cracking of the sealing beads.
It has been determined, especially for high temperature engineering plastics, that it is desirable that the bead be relatively narrow. That will enable the bead to be more conformable to mating surfaces. However as temperatures rise, as in the use of a head gasket, a narrow bead has less strength, and as a result maintaining a seal becomes more difficult. If a wider bead is used, at higher temperatures such a bead will eliminate creep relaxation. However a wide bead tends to be too stiff to allow proper sealing of the joint at room temperature. As such, delicate and careful balances are required, making effective sealing more difficult to accomplish than is desirable. Finally, although use of the recesses tends to reduce the difficulties in effecting a seal via a wide bead at room temperatures, it also sometimes allows too much creep relaxation at elevated temperatures.
Accordingly, it would be desirable to provide an engineering plastic gasket, such as a head gasket, having an integral sealing bead of improved sealing capacity at both low and high operating temperatures, and which is installed without requiring excessively high clamping loads.